The invention relates to an electronic apparatus whose power is supplied by a supply voltage, comprising a memory which contains electrically erasable data and a supply voltage detection device for detecting a variation of the supply voltage.
In heavily industrialized countries, a current tendency seeks to miniaturize the dimensions of portable telecommunication equipment intended for the public at large and for current use. The makers of this electronic equipment are thus exposed to heavy competition regarding the weight-to-volume ratio and the range of their apparatus. As the latest integrated circuit technologies currently permit of considerably reducing the volume of the electronic circuits, the range of this portable apparatus has become the factor which restricts this course to miniaturization. Indeed, generally intended for mobile use, this apparatus is fed by power supply batteries whose range is proportional to the weight in a given technology. In consequence, an apparatus fed by a battery is all the lighter as its range is smaller, which explains why the battery of a portable apparatus frequently turns out to be discharged.
Thus, to avoid certain phenomena which are likely to damage the apparatus, it is very important to anticipate during the discharging the instant at which the supply voltage will be cut off. Notably, the mobile radio telephones or other equipment comprising processors and electrically erasable memories of the EEPROM type (Electrically Erasable Programmable Read-only Memory) cannot withstand sudden power cuts. If the power supply is not cut off until its voltage drops below a threshold defined as critical by the manufacturer, the contents of the EEPROMs may be corrupted. In effect, the processor powered by an insufficient voltage no longer controls its addressing system. It runs the risk of writing an erroneous address in the EEPROM and overwriting the data which are found at that address. Data may then be lost, which is very harmful to the use of the radio telephone.
In a known electronic apparatus, a supply voltage detection device is used to periodically sound the supply voltage produced by the battery in order to detect the instant at which said voltage drops below the critical voltage and cut off the power supply so as not to change the data of the EEPROM.
An apparatus comprising such a supply voltage detection device, however, thus has a major drawback that questions its reliability. In effect, based on a periodic sounding technique, the detection precision and thus the reliability of this device directly depend on the sounding period used. As the conventional discharging curve of a battery drops very rapidly towards the end of the discharge, the power supply is frequently cut off which is undetected by the current device of which the sounding period is very large compared to the rapidity with which the voltage drops at the end of the discharge.
Diminishing the sounding period for enhancing the chances to detect the crossing of the critical threshold forms a too expensive solution which necessitates a faster and more powerful processor than that used in the known device.